One of the main goals of calcSD is to spread more accurate information about the average size to others in an organized and simple way. In here are a few links to other webpages that might be of help regarding this topic. Please do note that, while I like these resources enough to recommend them, they are not owned or coded by me, nor are the opinions expressed in them necessarily mine.
WARNING: Sites marked NSFW contain adult imagery.
Other percentile calculators:
This is but a simple page with only a few links. If you feel doubtful or unsure about anything, do not hesitate on searching more about it elsewhere on the internet.